Conventionally, as electrophotographic photoconductors for image-forming apparatuses and so on, organic photoconductors comprised of organic photoconductive materials such as charge transporting agents, chare generating agents, and binder resins. The organic photoconductor has the advantage of high flexibility in structural design because it can be easily manufactured and an appropriate photoconductive material can be selected from a variety of options, compared with the conventional inorganic photoconductors.
Among the organic photoconductive materials, for example, JP 2000-66419 A discloses a stilbene derivative compound as a charge transporting agent having high charge mobility, which is represented by the following general formula (74);
(wherein, B, C, D, E, F, and G respectively stand for benzene rings which may have substituents, among which at least one may have an alky group or the like; Y stands for a divalent aromatic hydrocarbon residue or the like which may have a substituent; R11, R12, R13, and R14 respectively stand for alkyl groups, aryl groups, or the like, which may have substituents; n1 and n2 respectively stand for integers of 1 to 4; and X1 and X2 respectively stand for groups represented by the following general formulas (75) and (76);—CR15═CR16CR17  (75)—CR18═CR19CR20  (76)(wherein R15, R16, R17, R18, R19, and R20 respectively stand for alkyl groups, aryl groups, or the like, which may have substituents.)
In addition, JP 03-149560 A discloses a stilbene derivative compound as a charge transporting agent having high charge mobility, which is represented by the general formula (77);
(wherein Y stands for an organic group such as a substituted or unsubstituted phenylene group, or an organic group represented by the formula (78) described below, and R21 to R26 respectively stand for substituted or unsubstituted aryl groups, alkyl groups, or the like)
(wherein Z stands for an oxygen atom, a sulfur atom, or the like, or an organic group represented by the following formula (79));
(wherein R27 and R28 respectively stand for alkyl groups, aryl groups, or the like.)
Here, the stilbene derivative compound disclosed in JP 2000-66419 A is defied as one having at least one alkyl group in the benzene rings B-G of the general formula (74). However, the stilbene derivative compound described in a concrete example has a central structure with a divalent phenyl group having a coupling hand at the para position, a divalent diphenyl group having coupling hands at the respective prara positions, or a divalent thiophene group in which a substituent on the benzene ring C is positioned at a meta position or a para position. Therefore, the concrete example of the stilbene derivative compound disclosed in JP 2000-66419 A shows poor compatibility with a binder resin and is difficult to uniformly disperse in a photoconductive layer. Therefore, there has been found a disadvantage in that the prolonged use of such a compound tends to cause crystallization. In other words, the disclosed stilbene derivative compound has a problem of insufficient charge mobility when it has been used as a charge transporting agent in a photoconductor for long periods of time in spite of showing high charge mobility in the initial stages.
Furthermore, in JP 2000-66419 A, there is another problem in that the desired stilbene derivative compound cannot be obtained in a stable manner because of low production efficiency in the process for producing a stilbene derivative compound.
Moreover, the stilbene derivative compound disclosed in JP 03-149560 A showed a problem of poor compatibility with a binder resin because of no substituent in the benzene ring in the form of a triphenylamine structure on the end of the molecule. Therefore, there is a problem in that the compound is not only hardly dispersed in the photosensitive layer uniformly but also subjected to be crystallized when it is used for long periods of time.
As a consequence, for solving the problems involved in the conventional stilbene derivative compounds and for providing a suitable compound as a hole transporting agent or the like of an electrophotographic photoconductor, the present invention intends to provide:
1) a specific stilbene derivative compound, which is capable of improving its photosensitive property for long periods of time;
2) a specific stilbene derivative compound, which is capable of effectively preventing the crystallization thereof for long periods of time;
3) a process for stable production of the specific stilbene derivative compound; and
4) an electrophotographic photoconductor having excellent photosensitive property for long periods of time, which is attained by containing the specific stilbene derivative compound.